The invention relates to essentially water-insoluble amphiphilic particles or molecules having predominantly hydrophilic and predominantly hydrophobic domains distributed anisotropically over their surface and a particle size ranging from 1 nm to 100 xcexcm, to methods for producing these particles or molecules and to the selective use of the particles or molecules.
The hydrophilic or hydrophobic behavior of a solid is determined essentially by the groups located at its surface. For example, particles or molecules, which have hydroxyl groups at the surface, usually are hydrophilic. Such a behavior is observed, for example, by finely divided silica, which has been obtained by precipitation or pyrolytic means. If, however, there are alkylsilyl groups or hydrocarbon groups, such as alkyl groups and, in particular, long-chain alkyl groups, at the surface of the particles or molecules, the particles have hydrophobic properties.
It has long been known that the hydrophilic or hydrophobic character of inorganic or organic particles or molecules can be varied. This can be done by adsorbing substances at the surface of a particle or molecule and especially by chemical reactions with reactive groups, which are at the surface of the particle or molecule. There is an extensive literature under the keyword xe2x80x9csilane adhesivexe2x80x9d. It deals with this state of the art, especially for treating glass surfaces with alkylsilyl compounds.
For example, in the German Offenlegungsschrift 23 13 073, a method is disclosed for chemically modifying the surfaces of inorganic hydroxyl group-containing solids with the distinguishing feature that alkyl chains, which have reactive hetero atoms, are linked chemically to these surfaces.
It is illuminating that, by such a modification of the surface, the suitability of solids, modified in this manner, to function as a stationary phase in chromatography can be influenced significantly, since the physical and chemical behavior of the modified solid, with respect to the mobile phase, is determined essentially by the properties at its surface. On the basis of the modifying reaction and the intended use, it may be assumed that the whole surface of the particles participates in the modifying reaction. If the modifying agent is used in a sub-stoichiometric amount, so that some of the reactive groups, which are at the surface of the particles, cannot be modified, it may be assumed that the modified groups are distributed randomly on the surface.
The object of the German Offenlegungsschrift 21 07 082 is a surface-treated powdered silicon dioxide with a surface area of at least 10 m2/g, which is characterized by the fact that it has a degree of hydrophobicity, measured by the methanol titration test, of 5 to 35. The methanol titration test, the result of which is also referred to as a methanol number, provides a frequently used parameter for determining the degree of hydrophobicity. The test is carried out by adding 0.2 g of the powder, which is to be tested, to 50 mL of water, which is in a conical 250 mL flask. If the powder has a hydrophobic surface, it is not wetted by the water and floats on the surface. Methanol is now added slowly from a burette, until the whole of the powder, which is to be tested, is wetted. The end point marks the point in the addition of methanol, at which practically the whole of the powder is suspended in the liquid. The methanol number is then the percentage of methanol in the liquid mixture of methanol and water when the end point is reached.
In the aforementioned German Offenlegungsschrift 21 07 082, the silicon dioxide powder is made hydrophobic by treating the surface with a silane, which contains groups, which are reactive with respect to the hydroxyl groups of the silica, as well as hydrophobic groups. By the reaction of the hydroxyl groups at the surface of the silicon dioxide with the reactive groups of the silane, the particles are modified in such a manner, that the hydrophobic groups of the silane are aligned on the outside. Methyltriethoxysilane is an example of such a reactive silane. It is also mentioned in this Offenlegungsschrift that the hydrophilic groups are distributed randomly, that is, that the coverage of the surface proceeds according to statistical laws, so that the probability of encountering a hydrophilic group or a hydrophobic group on the surface of a modified particle is the same everywhere and depends on the concentration of these groups.
In the German Offenlegungsschrift 31 32 370, a method is described for recovering tertiary crude oil by flooding with surfactants. For this method, an effective amount of a silicon dioxide, the surface of which is modified, is added to the surfactant-containing aqueous liquid.
It is a common feature of all of these modified particles of the state of the art that the hydrophilicity or hydrophobicity of the surface has been modified selectively, in order to provide the particles with certain properties, which are desirable in applications. These application properties are based, in particular, on the improved compatibility and wettability of the particles with or by the medium respectively, in which the particles are located. The solids, known from this state of the art and having modified surface properties, have hydrophobic or hydrophilic groups, which are distributed uniformly randomly, that is, isotropically on the surface of the particles. It is thus only possible to make a hydrophilic particle more or less hydrophobic or vice versa. This is shown by the distribution of the particles between two immiscible liquids. If a layer of hexane, as an example of a nonpolar liquid, is placed above a layer of water as a polar liquid, and pyrogenic silica, the surface of which is untreated, is added, the untreated pyrogenic silica, because of the presence of hydroxyl groups at its surface, is distributed almost exclusively in the water phase. If the silica is hydrophobized by one of the methods named above, so that practically all the hydroxyl groups are modified and any hydroxyl groups remaining are sterically shielded so that their contribution to the surface properties is negligible, a silica, so hydrophobized, is distributed practically exclusively in the hexane phase. However, if pyrogenic silica is hydrophobized only partially and to a different extent, the degree of hydrophobicity being determined, for example, by the methanol number, distributions between the two phases, which correlate with the degree of hydrophobization, are obtained.
The EP 0 156 270 A2 relates to particles, which are smaller than 100 xcexcm and are modified by hydrophilic and hydrophobic groups. The hydrophilic and hydrophobic groups are distributed anisotropically on the surface of the modified particles. The EP 0 156 270 A2 also relates to methods for producing such particles and to their use as surface-active products, especially for stabilizing or de-stabilizing emulsions and foams, as well as for recovering tertiary crude oil. One embodiment relates to particles, for which partial amounts of particles, modified hydrophobically, and partial amounts of particles, modified hydrophilically, are chemically linked together.
The FR 9406899 (EP 0 686 391 A1) discloses that polyalkylsilsesquioxanes, such as Tospearl(copyright) 103, 105, 108 (Toshiba), stabilize a water-in-oil emulsion. The surface of these particles has hydrophobic properties, the particles having alkyl chains containing up to 4 carbon atoms at the surface. The surface of these polyalkylsilsesquioxanes is dominated, on the one hand by the hydrophobic alkylsilyl groups and by a few hydrophilic SiOH groups. As the size of the particles increases, the hydrophobic character of the particles also increases. Likewise, the stabilizing effect of pyrogenic, hydrophobic silica, such as Aerosil(copyright) 974, 812 and 805 (Degussa), on water-in-oil emulsions is described. In this case, the diameter of the primary particles should be between 7 and 12 nm.
It is an object of the invention to produce associates or agglomerates of particles or molecules, which are hydrophilic or modified hydrophilically, and particles or molecules, which are hydrophobic or are modified hydrophobically, and optionally to isolate the associates or agglomerates and use them as emulsifiers for interfacial modifications, for example, water-in-oil or oil-in-water emulsions. Said particles or molecules should interact with one another over polar interactions or hydrogen bonds and these physical interactions should lead to new, inventive particles or molecules, which do not, however, exhibit any chemical linkage of partial amounts of the particles or molecules with hydrophobic or hydrophilic domains.
In a first embodiment of the invention, the objective above is accomplished by amphiphilic particles or molecules, which have a particle size of 1 nm to 100 xcexcm, are substantially insoluble in water, have predominantly hydrophilic and predominantly hydrophobic domains distributed anisotropically over their surface and consist of antagonistic partial amounts of particles or molecules, which in each case have predominantly hydrophilic or predominantly hydrophobic domains, the partial amounts of the particles or molecules being agglomerated or associated over polar interactions or hydrogen bonds.